Estimation of breeding values of Sahiwal cattle using test day milk yields.

Estimated breeding values of test-day (TD) and 305-day milk yield were calculated to compare ranking of animals on the basis of two information sources under an animal model. Two statistical models were used to analyze 780 first lactation (305-day) and monthly milk yield records. The first model was an individual animal model to analyze lactation milk yield with period-season of calving as fixed effect, while the second model was a repeatability model where monthly milk yield records were analyzed using periodseason of calving as fixed effect and animals’ additive genetic effect and permanent environmental effect as random factors. In this model, the age at calving, ratio of days in milk to 305-day (as linear and quadratic components) and their reciprocal logs were used as covariables. Ranking of animals for estimated breeding values from the two models was compared. The rank correlations were 0.927 and 0.923 for sires and cows, respectively. Largest rank shift measured in sires and cows showed that ranking of sire was affected less than that of cows. Phenotypic and genetic correlations did not show any clear pattern due to limited number of observations. Higher values of rank correlations suggested that TD milk yields could be used instead of 305-day lactation yields for genetic evaluation of sires and cows. Detailed studies involving larger data sets were however, suggested for validation of results.